Pract. Chem Flashcards
Organic compounds generally consist of
Carbon & hydrogen
Other elements which may be present in organic compounds are
Oxygen, nitrogen, halogen & sulphur
Lassaigne’s test is preferred to confirm the presence of
Nitrogen, chlorine, bromine, iodine, sulphur
Lassaigne’s extract is
Salt fused with sodium metal to prepare water soluble salt, also called sodium fusion extract
Sodium thiocyanate is formed when
Possible only when sodium metal is in little amount (nitrogen & sulphur, both are present)
Prussian blue precipitate indicates presence of
Nitrogen
Sodium extract formula
NaCN (sodium cyanide)
Oxidation state of iron in sodium hexacyanoferrate / sodium ferrocyanide
+2 {Na4[Fe(CN)6]}
Oxidation state of iron in Prussian blue
Ferric ferrocyanide [iron hexacyanoferrate]
Fe4[Fe(CN)6]3 => +3 & +2
Violet colour confirms the presence of
Sulphur
Sodium nitroprusside
Na4[Fe(CN)5NOS] - presence of sulphur
Black ppt of lead sulphide (Pbs) confirms the presence of
Sulphur
Formation of blood red colour confirms the presence of
Both nitrogen and sulphur
Appearance of blood red colour
Ferric sulphocyanide
Fe(SCN)3
White ppt which is soluble in ammonium hydroxide (insoluble in HNO3) confirms the presence of
Chlorine
Yellow ppt - partially soluble in ammonium hydroxide confirms the presence of
Bromine
Dark yellow ppt - insoluble in ammonium solution indicates the presence of
Iodine
In layer test (sodium fusion extract + ccl4+ Cl water)
Orange layer - presence of Br
Violet layer - presence of I
Ceric ammonium nitrate test confirms
(Red coloration) - alcoholic group
Lucas reagent (ZnCl2 + conc.HCl)
1° alcohol = no reaction
2° alcohol = turbidity within minutes
3° alcohol = immediate turbidity
Iodoform test - given by
Compounds having α- methyl group
Confirmation iodoform test
Yellow ppt of iodoform
Phenols form which coloured complex with freshly prepared FeCl3 solution
Violet
Violet/ blue coloration, given by
Resorcinol, o-, m-, p- cresol
Catechol gives which colour
Green (rapidly darkness)
1 and 2- naphthol - which colour
Do not show characteristic colour
Phenol condenses with phthalic anhydride in the presence of conc. H2SO4 to give
Phenolphthalein (gives dark pink colour with NaOH soln) — called phthalein dye test
2,4-DNP test
Yellow - aldehyde
Red - ketone
2, 4-DNP reacts with aldehyde and ketones to give
DNP( Hydrazone)
Schiffs test, felhings test, tollens test are given by
Aldehydes only
Felhings A
Aq. Cuso4
Felhings b
Alk. Sodium potassium tartarate (Rochelle’s salt)
Cupric ions of copper tartarate oxidises aldehydes to
Carboxylic acid (orange red ppt of Cu2O)
Ketone- unaffected
Aromatic aldehydes with felhings
Don’t give positive fehlings test
Benedict solution
Alk. (Copper sulphate+ sodium citrate)
More stable than fehlings solution & can be stored for longer duration
Schiffs test prepared by
Decolourising aq. Soln of p- rosaniline hydrochloride dye (adding sodium sulphite or passing SO2 gas in it)
Pink colour of schiffs indicate
Presence of aldehyde group
